Production of regenerated cellulose filaments



United States Fate-mt ()flice Patented Aug. 22, 1961 2,997,365PRODUCTIGN F REGENERATED CELLULOSE FILAMENTS John Oliver Smith,Coventry, and David Nicholson Tyler, Codsall, near Woverhampton,England, assignors to Courtaulds Limited, London, England, a Britishcomp y No Drawing. Filed July 30, 1959, Ser. No. 830,477 Claimspriority, application Great Britain Aug. 12, 1958 6 (Ilaims. (Cl. 18-54)This invention relates to the production of regenerated cellulosefilaments from viscose and in particular to a process for the productionof filaments having a high ratio of wet to dry tenacity, lowextensibility, no skincore differentiation and low water-imbibition.

We have found that by modifying or eliminating certain features of thebasic viscose rayon process, highly oriented viscose rayon textilefilaments having low extensibility can be produced.

The present process differs from the basic viscose rayon process in thefollowing respects (1) The use of a cellulose having a higher degree ofpolymerisation (D.P.). In practice this may lead to the elimination orshortening of mercerising or the ageing of the alkali cellulose.

(2) The use of a higher viscosity viscose. This is, to an extent,associated with the use of high D.P. cellulose, for only low celluloseconcentrations of about 3 percent in the viscose could be used if normalball-fall viscosities of, say, about 40 were to be used. However theincreased viscosity assists in the rapid coagulation of the viscoseduring spinning and this is advantageous. The maximum increase in theviscosity is determined practically by the ability of the spinningequipment to handle the viscose. Thus a cellulose concentration of from4 percent to 6 percent in the viscose and a viscose ball fall viscosityof over 50 and preferably from 100 to 200 may be used in practice.

(3) The use of a lower caustic soda concentration in the viscose whichenables a low acid coagulation bath to be used. Such a bath canco-operate in the rapid coagulation of the filaments, but only slowlyregenerates the cellulose. In practice the cellulose xanthate crumbs maybe mixed with water rather than with the caustic soda solutions ofnormal viscose manufacture.

(4) The spinning of viscoses having higher salt figures so that anunusually large concentration of cellulose xanthate is present in thefreshly extruded filaments and is preserved to a large extent in thefilaments during the stretching operation, the more plastic cellulosexanthate molecules allowing more applied stretch than the relativelyrigid regenerated cellulose molecules.

(5) The use of a coagulating bath containing much less acid, a lowersodium sulphate concentration and no zinc sulphate or only such zincsulphate as is inevitably present as an impurity and in any case notmore than 0.02 percent. The temperature of the bath should be between 20C. and 30 C., that is to say lower than usual. All of thesemodifications are calculated to reduce the rate of regeneration of thecellulose.

(6) The use of a greatly reduced immersion path of the filaments in thebath, only sufiicient to cause the filaments to coagulate so that theymay be drawn from the bath without damage whilst preserving, as much aspossible, the original xanthate groups of the viscose. The filaments arethen in the very plastic condition required for the stretch which isapplied outside the bath.

The necessary length of the immersion path varies with the denier of thefilaments being spun.

(7) The stretch of at least percent is applied to the filamentsimmediately they emerge from the bath. The plastic condition of thefilaments makes the application of such a large stretch relatively easyand the filaments are fully regenerated only after the stretch has beenapplied.

The invention accordingly consists in a process for the production ofviscose rayon filaments comprising extruding viscose having a cellulosecontent between 4 and 6 percent and a caustic soda content approximatelyhalf that of the cellulose, the cellulose having an average degree ofpolymerisation of at least 300 and the viscose having a salt figure ofat least 10 and a ball fall viscosity of at least 50, preferably betweenand 200, into a coagulating bath containing from 2.0 percent to 3.5percent of sulphuric acid, less than 15 percent and preferably between 1percent and 10 percent sodium sulphate, and not more than 0.02 percentof zinc sulphate as an impurity, maintaining the bath temperaturebetween 20 C. and 30 C., limiting the length of the immersion path sothat the filaments may be stretched by at least 80 percent of theiroriginal length on emerging from the bath, stretching the filamentsimmediately after they have emerged from the bath by at least 80 percentand subsequently completing the regeneration of the fila ments.

The required inmiersion path of the filaments in the bath varies withthe denier of the filaments. Thus for filaments having deniers up to 4.5the immersion path should not exceed 6 inches and it is preferred forfila: ments having deniers of 3 or less that the immersion path shouldnot exceed 3 inches.

The filaments can then be washed, dried and collected in a continuousform, or cut to produce a staple fibre, and subsequently washed anddried. Regeneration can be accelerated by treating the fibres at asuitable stage with warm dilute acid for example 2 percent of sulphuricacid at a temperature of 60 C.

The amount of sulphuric acid in the regenerating bath is kept within thestated range of 2.0 to 3.5 percent and it is preferably just sufiicientto secure adequate coagulation. The actual amount varies with the numberof filaments, the filament denier, spinning speed and the sodiumsulphate concentration in the bath.

The highly oriented filaments of low extensibility can be made intofabrics having good dimensional stability and this is mainly due to thelow imbibition of the filaments and their high initial wet modulus, thatis the markedresistance of the wet fibres to stretch under low loads.The fabrics show reduced relaxation shrinkages and greatly reduced oreliminated progressive shrinkages.

These properties of the fabrics are similar to or better than cottoncloths of the same construction and are markedly superior to similarfabrics made from commercially available viscose rayon filaments.

The invention is illustrated by the following examples in whichpercentages are by weight.

Example 1 A high quality wood pulp such as that sold under the tradename Cordenier J. was steeped in an 18.6 percent aqueous solution ofcaustic soda for 1 /2 hours at 19 C. The surplus solution was removed bysqueezing the pulp to a press ratio of 2.8 and the pulp was thendisintegrated into'crumbs for 2 /2 hours at 19 C. after which the crumbswere allowed to age for -17 hours at the same temperature. The alkalicellulose was then xanthated for 3 hours with 42 percent of carbondisulphide (calculated on the original alpha-cellulose content of thewood pulp) at 24 C. and the resulting xanthate was mixed in awater-cooled vessel at 15 C. The mixing time was 3 hours during whichthe temperature rose to :17 C. A further 10 percent of carbon disulphide(also based on the alpha-cellulose) was then added in the mixer and theviscose was then filtered, deaerated by a flash deaeration processandleft to age for 12 hours in vacuum.

The viscose, containing percent of cellulose, 2.4 percent of causticsoda and 2.1 percent of sulphur and at a salt figure of 15, was thenextruded at a ball fall viscosity of 100 seconds at 18 C. into aregenerating bath containing 2.7 percent of sulphuric acid and 1 percentof sodium sulphate at a temperature of 20 C. The viscose was extrudedvertically upwards into the bath through a jet the face of which wasabout 1 /2 inches below the surface.

The filament bundle travelled vertically upwards through the bath andthen a distance of inches through the air onto two skewed sets ofconcentric discs of diameters 5, 6, 7, 8 and 9 inches respectively,giving 80 percent stretch for four stages. From the last disc the bundlewas taken up on a roller and was stretched a further 17 percent betweenthe last'disc and the roller. It was then passed through a hot fixingbath containing 2 percent of sulphuric acid at a temperature of 90 C. inwhich it was stretched a further 3 percent. After washing and drying,the filaments had the following properties:

Filament denier 1.5 Conditioned tenacity grams per denier 3.6 Wettenacity, do 2.6 Extensibility conditioned percent 6.0 Extensibility wetdo 8.0 Water imbibitinn d0 65.0

The crosssection of the filaments was circular and no differentiationbetween skin and core could be detected upon staining.

Example 2 Viscose prepared as inExample l was spun through 3 mildiameter holes into a bath containing 2.5 percent of snlphuric acid and5.3 percent of sodium sulphate at a temperature of 23 C., the immersionbeing two inches. The thread wasstretched a total of 100 percent in twostages and was then fully regenerated, washed, dried and collected. Thefinal spinning speed was 50 metres per minute. The filaments producedhad the following properties:

Denier 1.84 Conditioned tenacity grams per denier 3.62 MM tenacity m---2.46 Extensibility conditioned percent 8.3 Extensibility wet do 10.6

Water imbibitinn dn 75.0

The cross-section was circular and showed no skincore differentiation onstaining.

Example 3 spinning speed being. m./rninute. The filament denier was 1.5and the average properties of randomly chosen filaments were:

Conditioned tenacity "grams per denier 4.31 Conditioned extensibilitypercent 8.0 Wet tenacity grams per denier 3.05 Wet extensibility percent10.4 Water imbibition do 74.0

Example 4 and the denier 1.5. The filaments were cut to a staple lengthof 1 inches, Washed and dried. The average properties of the fibreswere:

Conditioned tenacity 2.90 Conditioned extensibility percent 12.5 Wettenacity 1.80 Wet extensibility percent 14.8

The staple fibres were spun into a yarn of 1/l8s cotton count which waswoven into a cloth of construction 64 ends/54 picks. 10 pounds of thiscloth was washed in soap at 60 C. in a rotary washing machine for 30minutes, rinsed for 5 minutes at 40 C., rinsed again for 10 minutes at40 C., hydroextracted and dried in a tumbler drier. The laundering cyclewas repeated at number of times and the dimensions of the cloth measuredat intervals. The results are shown in the following table.

Percent shrinkage Water imbibi- Wash tion (percent on weight Warp Weftof fabric) 1 loose dried 1. 4 4. 0 +1. 2 l. 4 4. 2 1. 8 0. 6 1.0 4. G5.0 1. 0 1. 8

It will be noted that the properties of the fabric are equivalent to orbetter than cotton in a cloth of the same construction and are muchimproved compared with normal viscose rayon textile fibres in a cloth ofthe same construction.

What we claim is:

1. A process for the production of viscose rayonfilaments comprisingextruding viscose having a cellulose content between 4 and 6 percent anda caustic soda content approximately half that of the cellulose, thecellulose having an average degree of polymerization of at least 300 andthe viscose having a salt figure of at least 10 and a ball fallviscosity between about 50 and about 200 seconds at 18 G, into acoagulating bath containing from 2.0 percent to 3.5 percent of sulphuricacid, less than 15 percent sodium sulphate, and not more than 0.02percent of zinc sulphate as an impurity, to form filaments, maintainingthe bath temperature between 20 C. and 30 C., removing the filamentsfrom the bath while they are still capable of being stretched in air atleast 80% of their original length, stretching the filaments in airimmediately after they have been removed from the bath by at least 80%and completing the regeneration of the filaments after they have beenstretched.

2. Aprocess for the production of viscose rayon filaments having deniersof up to 4.5 according to claim 1, in which the length of the immersionpath of the filaments in the bath is not more than 6 inches.

2,997,365 5 6 3 A process for the production of viscose rayon fila- 6. Aprocess as claimed in claim 1 in which the salt ments having deniers ofup to 3 according to claim 1, in figure of the viscose is at least 12.which the maximum length of the immersion path of the filaments in thebath is 3 inches References Cited in the file of this patent 4. Aprocess as claimed in claim 1 in which the bath 5 UNITED STATES PA ENTScontains from 1 percent to 10 percent of sodium sulphate. 2,611,923Marion Sept 30, 1952 5. A process as claimed in claim 1 in which theball 2,732,279 Tachikawa Ian. 24, 1956 fall viscosity of the viscose isbetween 100 and 200. 2,775,505 Pedlow Dec. 25, 1956

1. A PROCESS FOR THE PRODUCTION OF VISCOSE RAYON FILAMENTS COMPRISINGEXTRUDING VISCOSE HAVING A CELLULOSE CONTENT BETWEEN 4 AND 6 PERCENT ANDA CAUSTIC SODA CONTENT APPROXIMATELY HALF THAT OF THE CELLULOSE, THECELLULOSE HAVING AN AVERAGE DEGREE OF POLYMERIZATION OF AT LEAST 300 ANDTHE VISCOSE HAVING A SALT FIGURE OF AT LEAST 10 AND A BALL FALLVISCOSITY BETWEEN ABOUT 50 AND ABOUT 200 SECONDS AT 18* C., INTO ACOAGULATING BATH CONTAINING FROM 2.0 PERCENT TO 3.5 PERCENT OF SULPHURICACID, LESS THAN 15 PERCENT SODIUM SULPHATE, AND NOT MORE THAN 0.02PERCENT OF ZINC SULPHATE AS AN IMPURITY, TO FORM FILAMENTS, MAINTAININGTHE BATH TEMPERATURE BETWEEN 20* C. AND 30* C., REMOVING THE FILAMENTSFROM THE BATH WHILE THEY ARE STILL CAPABLE OF BEING STRETCHED IN AIR ATLEAST 80% OF THEIR ORIGINAL LENGTH, STRETCHING THE FILAMENTS IN AIRIMMEDIATELY AFTER THEY HAVE BEEN REMOVED FROM THE BATH BY AT LEAST 80%AND COMPLETING THE REGENERATION OF THE FILAMENTS AFTER THEY HAVE BEENSTRETCHED.